Separation and purification
Introduced| English | Meaning |
|---|---|
| separation techniques/ˌsepəˈreɪʃn tekˈniːks/ | separation techniques |
| filtration/fɪlˈtreɪʃn/ | Separating insoluble particles from a fluid by passing the mixture through a porous barrier. |
| crystallisation/ˌkrɪstəlaɪˈzeɪʃn/ | Formation of solid crystals from a solution or another phase; used here to obtain a dissolved solid from its solution. |
| simple distillation/ˈsɪmpl dɪstɪˈleɪʃn/ | Separating a volatile liquid by vaporising it and condensing its vapour; used here to recover solvent from a nonvolatile solute. |
| fractional distillation/ˈfrækʃənl dɪstɪˈleɪʃn/ | Separating components of a liquid mixture through repeated evaporation and condensation based on differences in volatility. |
Getting pure substances
- Mixtures are everywhere, but chemists often need a pure substance.
- Several separation techniques 分离技术 do the job, each suited to a different mixture.
Separation method lab
Choose the method that matches the mixture.
Filtration is used to separate:
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Filtration removes insoluble solids.
To recover a dissolved solid from its solution, you use:
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Evaporate the solvent and crystallise the solid.
Filtration 过滤 and crystallisation 结晶
- Filtration separates an insoluble solid from a liquid.
- Crystallisation gets a dissolved solid back by evaporating the solvent.
Filtration separates an insoluble solid (residue) from a liquid (filtrate)
Pure water can be separated from salt water by:
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Distillation boils off and condenses the water.
Fractional distillation separates an insoluble solid from a liquid.
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False. That is filtration. Fractional distillation separates liquids with different boiling points, such as crude oil fractions or ethanol and water.
Distillation
- Simple distillation 蒸馏 separates a solvent from a solution (e.g. pure water from salt water).
- Fractional distillation 分馏 separates liquids with different boiling points (e.g. crude oil, alcohol from water).
Fractional distillation adds a fractionating column, so liquids with different boiling points separate cleanly
An insoluble solid is separated from a liquid by ______.
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Filtration traps the solid.
Choosing the method
- Pick the technique by what you want to separate.
- Insoluble solid → filter; dissolved solid → crystallise; liquids → distil.
Worked example. To get pure water from salt water, use simple distillation: the water boils off, is condensed and collected, leaving the salt behind. The right method depends on the mixture.
You've got it
- filtration removes an insoluble solid; crystallisation recovers a dissolved solid
- simple distillation separates a solvent; fractional distillation separates liquids by boiling point
- choose the method to match the mixture
Write from distillation collecting the water
- A solution of salt in water is to be separated so that pure water is collected.
- The salt is dissolved, not sitting as a solid on the bottom.
Which method collects the pure water?
The solvent is boiled off and condensed.
How is pure water collected from salt water?
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Water vapour leaves the dissolved salt behind.